Webbing Retractor

ABSTRACT

A webbing retractor  10  has a structure in which a housing  48,  to which a motor  44  is attached, faces in an axial direction of a worm gear  34,  and is assembled and fixed to an end face of a case  30  which is orthogonal to a direction of thickness of the case  30,  in which a clutch  26  which is attached in a joined state to a side face of one leg plate  16  is accommodated, and at an opposite side from a back plate  14.  Moreover, this is a structure in which a rotation shaft of the motor  44  is between the leg plate  16  and a leg plate  18  in a state of being orthogonal to a winding shaft  20,  and the motor  44  is disposed directly below the winding shaft  20.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a webbing retractor, and particularly relates to a webbing retractor which is capable of winding up a webbing by rotating a winding shaft with a motor.

2. Description of the Related Art

A seat belt apparatus for restraining a vehicle occupant is provided with a webbing retractor (webbing winding device). At this webbing retractor, a tension reducer mechanism, for alleviating or eliminating an excessive sense of pressure during wearing of the webbing, and/or a pretensioner mechanism may be provided. A pretensioner mechanism eliminates a slight looseness, which is referred to as ‘slackness’ or the like, by winding up a certain amount of the webbing belt onto the winding shaft during a state of rapid vehicle acceleration/deceleration and increases a restraining force on the body of the vehicle occupant from the webbing belt, and more assuredly retains the body of the vehicle occupant. Further, a structure known as a motor retractor, which performs the above-described various functions with a motor, is known (see, as examples, Japanese Patent Application Laid-Open (JP-A) No. 2001-130376 and JP-A No. 2001-347923).

With this kind of motor retractor, in addition to being capable of exhibiting the functions of, for example, the tension reducer and pretensioner as described above, it is also possible to implement winding-up of the webbing at usual times of wearing of the webbing, and assistance for drawing-out and the like, which is extremely advantageous.

In particular, in recent years, for a motor retractor as described above, a structure has been proposed which detects a distance to another vehicle in front or an obstacle with a forward observation device such as a distance sensor or the like, causes the motor to operate when the distance to the vehicle in front or obstacle is less than a certain value, and causes the winding shaft to rotate in a winding direction with rotation force of the motor.

In a case of a motor retractor as described above, in order to prevent transmission of rotation from the winding shaft side to the motor, a clutch is interposed between an output shaft of the motor and the winding shaft, and a structure which transmits only rotations from the motor output shaft side to the winding shaft is formed by this clutch.

With a conventional motor retractor of this form, it is necessary to dispose the clutch at a position corresponding to an end portion of the winding shaft. Therefore, this clutch apparatus is disposed at an outward side of a pair of leg plates which structure a frame. Moreover, this has been a structure in which the motor is disposed at the outward side of the leg plate at the side at which this clutch is provided (that is, disposed as same as the clutch), or has been a structure in which the motor is disposed upward or downward of the frame relative to the pair of leg plates. In a case with such a structure, because components which are comparatively large and heavy, such as the motor, are located at the outward side and upward or downward of the frame, there have been drawbacks in that the motor retractor as a whole becomes larger, in addition to which weight balance of the motor retractor as a whole becomes poor. Further still, at a motor retractor of this form, when the motor retractor vibrates, a torsion force is applied to a case of the clutch apparatus and/or the frame by heavy components such as the motor, and it is necessary to assure a rigidity capable of withstanding this.

SUMMARY OF THE INVENTION

In consideration of the circumstances described above, the present invention provides a webbing retractor which, in addition to being capable of rotating a winding shaft with a motor, is compact and has good weight balance and, moreover, has higher rigidity.

An aspect of the present invention is a webbing retractor including: a frame formed of a pair of leg plates facing one another and a back plate, the frame being a single body at which the pair of leg plates are continuous with the back plate; a winding shaft which is rotatably supported between the pair of leg plates with an axial direction thereof being along a direction of facing of the pair of leg plates, at which a base end portion of a webbing belt for restraining a vehicle occupant is engaged, and which winds up the webbing belt by rotation in one direction about its axis; a gear housing; a motor attached at the gear housing, which is disposed between the pair of leg plates in a state in which a rotation shaft thereof is orthogonal to the winding shaft; a motor gear section accommodated in the gear housing, which is formed of a plurality of spur gears, axes of which are disposed parallel with the rotation shaft of the motor, and which are coupled with the rotation shaft of the motor; a clutch case attached in a joined state at a side face of any one leg plate of the pair of leg plates; a clutch accommodated in the clutch case, which is mechanically interposed between the motor and the winding shaft, which transmits rotation of the motor to the winding shaft and causes the winding shaft to rotate, and which blocks transmission of rotation which occurs at the winding shaft side and prevents this rotation being transmitted to the motor; and a clutch gear section accommodated in the clutch case, the clutch gear section comprising a worm gear, an axis of which is disposed parallel with the rotation shaft of the motor and which is detachably coupled with a final spur gear of the motor gear section, and a worm wheel, which is disposed coaxially with the winding shaft, meshes with the worm gear and transmits rotation force of the worm gear to the clutch, wherein the gear housing faces in an axial direction of the worm gear, and is assembled and fixed to an end face of the clutch case which is orthogonal to a direction of thickness of the clutch case, at a side which is opposite from the back plate.

With the webbing retractor of the present aspect, a vehicle occupant sits on a seat of a vehicle, wraps the webbing belt around the body, and puts the webbing belt into a state of being worn on the vehicle occupant's body by, for example, engaging a tongue plate provided at the webbing belt with a buckle apparatus.

When, for example, there is an obstacle forward of the vehicle during running of the vehicle, and a separation between the vehicle and the obstacle (a distance from the vehicle to the obstacle) reaches to within a predetermined range, driving of the motor is commenced. The plurality of spur gears of the motor gear section is coupled to the rotation shaft of the motor. Further, the worm gear of the clutch gear section is coupled to the final spur gear of the motor gear section, and the worm wheel meshes with this worm gear. Consequently, when the motor drives, driving force thereof is transmitted to the clutch by the plurality of spur gears of the motor gear section, and the worm gear and worm wheel of the clutch gear section. Further, rotation force is transmitted through the clutch to the winding shaft, and the winding shaft is rotated in a webbing winding direction. As a result, the webbing belt is wound up onto the winding shaft from a base end side, a slight slackness, known as ‘slack’, of the webbing belt in the state of being worn is eliminated, and a restraining force on the body of the vehicle occupant from the webbing belt can be raised.

In the webbing retractor of the present aspect, the clutch case, which accommodates the clutch and the clutch gear section, is attached in a joined state at a side face of either one leg plate of the pair of leg plates, which structure the frame for supporting the winding shaft. Moreover, this is a structure in which the motor is disposed between the pair of leg plates in a state in which the rotation shaft thereof is orthogonal to the winding shaft. Therefore, compared with a structure in which the motor is disposed at an outer side of the frame, this webbing retractor can be vastly made compact in overall size. That is, because this is a structure in which a comparatively large component, such as the motor, is disposed between the pair of leg plates, the motor, which is the large component, will not protrude outward from the leg plates. Space between the pair of leg plates can be effectively utilized, and the retractor as a whole can be made compact. Furthermore, because this is a structure in which, as described above, the motor is disposed between the pair of leg plates, compared with a structure in which the motor is disposed at an outer side of the frame, an overall weight balance of the webbing retractor can be made to approach the middle in the direction of facing of the leg plates. Accordingly, the webbing retractor can be stabilized weightwise.

Further, this is a structure in which the clutch and clutch gear section are accommodated in the clutch case which is attached to the side face of the one leg plate in the joined state and, moreover, the motor is disposed between the pair of leg plates. Consequently, the motor and the clutch can be disposed close together. As a result, even with the structure in which the output shaft of the motor and the clutch are mechanically coupled by the plurality of spur gears, the worm gear and the worm wheel, structure of a driving force transmission mechanism and the like can be made simple. As a result, the retractor can be made more compact and, furthermore, costs can be made cheaper.

Further, this is a structure in which a component which is comparatively heavy, such as the motor, is disposed between the pair of leg plates. Therefore, rather than just one or other of the leg plates and the back plate joining these leg plates, the motor can be supported by, as necessary, any two or all of the pair of leg plates and the back plate joining these leg plates. As a result, there is no necessity to particularly improve strength of respective members of the retractor for supporting the motor and, as a result thereof, it will be possible to achieve a reduction in weight of the retractor and a reduction in costs.

The final spur gear of the motor gear section and the worm gear of the clutch gear section are detachably coupled. Therefore, it is possible to detach and replace the motor gear section independently of the clutch gear section. Accordingly, it is possible to, for example, easily replace and employ different motor gear sections, in which tooth counts of the plurality of spur gears, and numbers thereof and the like are altered. Thus, it is possible to easily alter and specify a transmission ratio (reduction ratio) of driving force which is transmitted from the motor to the clutch, and it will be possible to easily implement specification and alteration of a speed of rotation transmitted to the clutch when the motor drives, and hence of a speed of rotation of the winding shaft (specification of variations in webbing winding characteristics).

Further, since it is possible to detach and replace the motor gear section independently of the clutch gear section, even in a case of replacing and altering the motor gear section for alteration of the transmission ratio (reduction ratio) as described above or the like, neither of a meshing state of the plurality of spur gears of the motor gear section and a meshing state of the worm gear and worm wheel of the clutch gear section will be altered (no effect will be applied). Accordingly, there will be no alteration in meshing accuracy of the respective teeth (gears), and there will be no reduction (deterioration) in efficiency of transmission of the driving force.

When this webbing retractor vibrates, twisting force is applied to the above described clutch case and/or the one leg plate to which the same is attached in the joined state, due to heavy components such as the motor.

In this respect, the webbing retractor of the first aspect is a structure in which the gear housing, to which the motor is attached, faces in the axial direction of the worm gear, and is assembled and fixed to the clutch case end face, which is orthogonal to the thickness direction of the clutch case which is attached to the side face of the one leg plate in the joined state, at the opposite side from the back plate (i.e., the clutch case end face which is parallel with the back plate and at the opposite side from the back plate). Consequently, rigidity in the direction of thickness of the clutch case and a direction intersecting therewith is higher, and it is possible to reliably withstand even torsion forces at the aforementioned times of vibration and the like.

Further yet, this is a structure in which, of the plurality of spur gears of the motor gear section accommodated in the gear housing, the final spur gear is coupled with the worm gear of the clutch gear section, and the gear housing is a structure which is assembled and fixed to face in the direction intersecting the thickness direction of the clutch case, that is, to face in the axial direction of the worm gear. Therefore, dimensional variations in a direction of assembly of an assembly fixing portion of the gear housing will not affect a pitch (meshing state) of the final spur gear, which is coupled with the worm gear, with the other spur gears. Accordingly, there is no alteration in meshing accuracy of the respective teeth (gears), and there is no reduction (deterioration) in efficiency of transmission of the driving force.

As described above, the webbing retractor relating to the present invention has excellent effects in that, in addition to being able to rotate a winding shaft with a motor, it is compact and weight balance is good and, moreover, rigidity is higher.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing overall structure of a webbing retractor relating to an embodiment of the present invention.

FIG. 2 is an exploded perspective view showing structural structure of a motor and motor gear section of the webbing retractor relating to the embodiment of the present invention.

FIG. 3 is a perspective view showing structure of an assembly fixing of the motor and motor gear section of the webbing retractor relating to the embodiment of the present invention.

FIG. 4 is a perspective view showing overall structure of the webbing retractor relating to the embodiment of the present invention.

FIG. 5 is a perspective view showing structure of a motor driving force transmission system of the webbing retractor relating to the embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, overall structure of a webbing retractor 10 relating to an embodiment of the present invention is shown in an exploded perspective view. In FIG. 2 and FIG. 3, structures of principal components of this webbing retractor 10 are shown in exploded perspective views. Further, in FIG. 4, overall structure of the webbing retractor 10 is shown in a perspective view, and in FIG. 5, structures of principal components of the webbing retractor 10 are shown in a perspective view.

The webbing retractor 10 is provided with a frame 12. The frame 12 is structured by a substantially plate-form back plate 14 and a leg plate 16 and leg plate 18 pair, which extend integrally from two width direction ends of this back plate 14. This is a structure in which the back plate 14 is attached to a vehicle body by being fixed to the vehicle body with unillustrated fastening means such as bolts or the like.

A winding shaft 20, which is fabricated by die-casting or the like, is rotatably disposed between the leg plate 16 and leg plate 18 pair of the frame 12. As a whole, the winding shaft 20 forms a spool (bobbin) shape and has a base end portion of a webbing belt (not shown), which is formed in a long belt shape, connected and fixed. When the winding shaft 20 is rotated one way about the axis thereof (hereafter, this direction is referred to as a ‘winding direction’), the webbing belt is wound up, from the base end side thereof, in a layered form at an outer peripheral portion of the winding shaft 20. On the other hand, if the webbing belt is pulled on from a distal end side thereof, the winding shaft 20 rotates accordingly while the webbing belt is drawn out (hereafter, the direction of rotation of the winding shaft 20 when the webbing belt is drawing out is referred to as a ‘drawing-out direction’).

One end side of the winding shaft 20 passes through the leg plate 18 and protrudes to the exterior of the frame 12. A locking mechanism, which is omitted from the drawings, is disposed sideward of the leg plate 18. The locking mechanism is structured to include an acceleration sensor, and links with a lock plate 22, which bridges across between the leg plate 16 and the leg plate 18, and a torsion bar 24, which is provided at an axial center portion of the winding shaft 20. This is a structure in which, at a time of rapid acceleration/deceleration of the vehicle or the like, one end of the torsion bar 24 is restrained, via the lock plate 22, by operation of the locking mechanism, and energy absorption is implemented while drawing-out direction rotation of the winding shaft 20 is blocked.

Meanwhile, a coupling screw 21 is attached at the other end side of the winding shaft 20. This coupling screw 21 passes through the leg plate 16 and protrudes outward of the frame 12. Further, a clutch 26 and a clutch gear section 28 are disposed at an outer side of the leg plate 16.

The clutch 26 and the clutch gear section 28 are structured to both be accommodated inside a case 30, which serves as a clutch case, and the clutch 26 is connected to the coupling screw 21. Further, the clutch 26 links with a gear wheel 32, which structures the clutch gear section 28. This gear wheel 32 is formed as a so-called wormwheel, at which wormwheel teeth are formed at an outer peripheral edge. The gear wheel 32 is disposed coaxially with the winding shaft 20, and this gear wheel 32 is mechanically connected to the coupling screw 21 (that is, to the winding shaft 20) via the clutch 26. Therefore, this is a structure in which, when the gear wheel 32 rotates, driving force is transmitted via the clutch 26 and the winding shaft 20 rotates in the winding direction, and transmission of a rotation which occurs at the winding shaft 20 side is blocked and transmission of this rotation to the gear wheel 32 is prevented. Further, a distal end of the coupling screw 21 which is connected to the clutch 26 passes through this clutch 26 and protrudes sideward.

Further, a worm gear 34 which structures the clutch gear section 28 is provided in the case 30. At the worm gear 34, an axis thereof is arranged in a state which is orthogonal to the winding shaft 20, an end portion thereof is supported at the case 30 via bushes 36 and 37, and it meshes with the gear wheel 32. One end side of the worm gear 34 is provided protruding outward from the case 30. Further, at a bearing portion of the case 30 which supports a distal end portion of the worm gear 34, a steel ball 38 is accommodated and touches a distal end portion of the worm gear 34, and an adjustment screw 40 is screwed in. The adjustment screw 40 pushes against the steel ball 38 with a distal end portion thereof, and thus the steel ball 38 is pushed against the distal end of the worm gear 34. As a result, axial direction displacement of the worm gear 34 is restricted (thrust-regulated). This is a structure in which the gear wheel 32 is rotated by this worm gear 34 rotating.

The case 30 which accommodates the clutch 26 and the clutch gear section 28 with the structures described above is covered by a clutch cover 31.

Thus, this is a structure in which the clutch 26 and the clutch gear section 28 are integrally assembled in the single case 30, and are formed as a whole into a unit.

A spring complete 42 is disposed sideward of the clutch 26 and clutch gear section 28 (the case 30). The spring complete 42 accommodates a spiral spring (not shown) thereinside. Of this spiral spring, a spiral direction outer side end portion is anchored at a main body of a case of the spring complete 42, and a spiral direction inner side end portion is anchored at a distal end of the coupling screw 21, which is passed through the clutch 26, and urges the winding shaft 20 in the winding direction.

Meanwhile, a motor 44 and a motor gear section 46 are disposed downward of the winding shaft 20 between the leg plate 16 and the leg plate 18.

As shown in FIG. 2, the motor 44 and the motor gear section 46 are provided with a housing 48, which serves as a gear housing. The motor 44 is attached with screws 47 at one side of this housing 48, and the motor gear section 46 is provided at another side of the housing 48. At the motor 44, a distal end side (output side) of a rotation shaft thereof is fixed at one side of the housing 48 in a state of being oriented to the housing 48, and the distal end (output side) of the rotation shaft passes through the housing 48 and protrudes to another side thereof (the side of the motor gear section 46).

Meanwhile, at the distal end of the rotation shaft of the motor 44 which protrudes to the other side (the motor gear section 46 side) of the housing 48, a pinion 72, which structures a plurality of spur gears of the motor gear section 46, is attached. Further, at the motor gear section 46, a gear 74 and a gear 76 structuring the driving force transmission mechanism, which are respectively formed as outward teeth spur gears, are accommodated in a state of meshing with one another. At this gear 74 and gear 76, axes thereof are both arranged parallel with the rotation shaft of the motor 44, and the gear 74 meshes with the pinion 72. The gear 76, which serves as a final spur gear, is separably coupled to one end portion of the worm gear 34, which protrudes outward from the case 30 of the clutch gear section 28 described above. Therefore, this is a structure in which, when the motor 44 rotates, driving force is transmitted through the pinion 72, the gear 74 and the gear 76, and the worm gear 34 is rotated. (See FIG. 5)

Further, this pinion 72, gear 74 and gear 76 are covered by a gear cover 78, which is attached to the housing 48. Pawl portions 80 are provided at the gear cover 78. The gear cover 78 is fixed to the housing 48 by these pawl portions 80 fitting and anchoring at pawl-holding portions 82, which are provided at the housing 48.

Thus, this is a structure in which the motor 44 and the motor gear section 46 are all integrally assembled in the single housing 48, and are formed as a whole into a unit.

The motor 44 and motor gear section 46 with the structures described above are separably attached, at mounting stays 84 which are integrally provided at the housing 48, by being fixed with screws 86 to the case 30 accommodating the clutch 26 and the clutch gear section 28 (that is, to the frame 12).

As is also shown in FIG. 2 and FIG. 3, positioning bosses 85, which serve as a positioning portion, are protrudingly formed at the mounting stays 84. Further, at an end face of the case 30 which is parallel with the back plate 14 (i.e., which is orthogonal to a thickness direction of the case) and at a side opposite from the back plate 14, positioning holes 87, which serve as a positioning holding portion, are formed to correspond with the positioning bosses 85. That is, this is a structure in which, by the positioning bosses 85 being fitted into the positioning holes 87 and the mounting stays 84 fastening and fixing to the case 30 with the screws 86, an assembly position of the housing 48 (i.e., the motor 44 and the motor gear section 46) with respect to the case 30 (that is, the frame 12) is uniquely specified. The housing 48 is assembled and fixed to face in the axial direction of the worm gear 34.

In a state of attached mounting of the housing 48 to the case 30 (the frame 12), the motor 44 is in a state in which the rotation shaft is orthogonal to the winding shaft 20 and the output side thereof is oriented toward a side opposite from the back plate 14 of the frame 12. Moreover, this is a structure in which the motor 44 is located between the leg plate 16 and leg plate 18 pair and, is located directly below the winding shaft 20.

Further, here, at the motor 44 and motor gear section 46 of the structure as described above, the gear 76 which serves as the final spur gear of the motor gear section 46 is detachably coupled with the worm gear 34 of the clutch 26 and clutch gear section 28. Moreover, the housing 48 (the mounting stays 84) is separably attached to the case 30 by the screws 86. Therefore, this is a structure such that, by removing the screws 86 and removing the housing 48 from the case 30, it is possible to detach the motor 44 and the motor gear section 46, still in an assembly state, from the case 30 (the frame 12).

Further, the motor 44 described above is structured to be operated on the basis of, for example, detection signals of a forward observation device or the like.

Next, operations of the present embodiment will be described.

With the webbing retractor 10 of the structure described above, a vehicle occupant sits on a seat of a vehicle, wraps the webbing belt around their body, and enters a state of the webbing belt being worn on the vehicle occupant's body by, for example, engaging a tongue plate provided at the webbing belt with a buckle apparatus.

In this state of the webbing belt being worn, even when winding/drawing-out of the webbing belt which is caused by movement of the body of the vehicle occupant or the like is implemented, that is, even when the winding shaft 20 rotates in the winding direction or the drawing-out direction, because of the clutch 26, there is no transmission of rotation force of this winding shaft 20 to the rotation shaft of the motor 44.

On the other hand, when, for example, there is an obstacle forward of the vehicle during running of the vehicle, and a separation between the vehicle and the obstacle (a distance from the vehicle to the obstacle) reaches to within a predetermined range, driving of the motor 44 is commenced and the rotation shaft is rapidly rotated.

When this rotation shaft of the motor 44 is rotated, rotation force thereof is transmitted to the clutch 26 by the pinion 72, gear 74 and gear 76 of the motor gear section 46, and the worm gear 34 and gear wheel 32 of the clutch gear section 28. Further, the rotation force is transmitted through the clutch 26 to the winding shaft 20, and the winding shaft 20 is rotated in the webbing winding direction. As a result, slackness of the webbing belt is eliminated, and a restraining force on the body of the vehicle occupant from the webbing belt can be raised. Temporarily, even if the vehicle occupant performs an operation of emergency control of the vehicle (emergency braking) thereafter, and the vehicle enters a rapid deceleration condition, the webbing belt can reliably retain the body of the vehicle occupant.

Further, when the motor 44 stops in a state in which the slackness has been eliminated thus, mechanical coupling of the rotation shaft of the motor 44 with the winding shaft 20 is released.

Here, in the webbing retractor 10 of the present embodiment, of the pair of leg plates 16 and 18 structuring the frame 12 for supporting the winding shaft 20, at a side face of one leg plate 16, the case 30 accommodating the clutch 26 and the clutch gear section 28 is attached in a joined state. Moreover, this is a structure in which the motor 44 is between the leg plate 16 and the leg plate 18, with the rotation shaft of the motor is orthogonal to the winding shaft 20, and is disposed directly below the winding shaft 20. Therefore, compared with a structure in which the motor 44 is disposed at an outer side of the frame 12, this webbing retractor 10 can be made compact in overall size. That is, it is a structure in which a comparatively large component, such as the motor 44, is between the leg plate 16 and leg plate 18 pair and is disposed directly below the winding shaft 20. Therefore, the motor 44, which is the large component, will not protrude outward from the frame 12 (the leg plates 16 and 18). As a result, space between the pair of the leg plate 16 and the leg plate 18 can be effectively utilized, and the retractor as a whole can be made more compact. Further, compared with a structure in which the motor 44 is disposed at an outer side of the frame 12, an overall weight balance of the webbing retractor 10 can be made to approach the middle in the direction of facing of the leg plate 16 and the leg plate 18, and the webbing retractor 10 can be stabilized weightwise.

Further, in the webbing retractor 10 relating to the present embodiment, this is a structure in which the clutch 26 and the clutch gear section 28 are accommodated in the case 30 which is attached to the side face of the one leg plate 16 in the joined state and, moreover, the motor 44 is between the pair of leg plates 16 and 18 and is disposed directly below the winding shaft 20. Therefore, the motor 44 and the clutch 26 can be disposed close together. Moreover, an output side of the rotation shaft of the motor 44 is disposed oriented toward an opposite side from the back plate 14 of the frame 12. Therefore, it is possible to arrange the motor gear section 46 and clutch gear section 28 (driving force transmission means) coupling the motor 44 with the clutch 26 without difficulty. Accordingly, structures of the motor gear section 46 and the clutch gear section 28 can be made simpler. In this respect too, the retractor can be made more compact and, further, costs can be made cheaper.

Further, this is a structure in which a component which is comparatively heavy, such as the motor 44, is between the pair of leg plates 16 and 18 and is disposed directly below the winding shaft 20. Therefore, rather than just one or other of the respective leg plates 16 and 18 and the back plate 14 which joins these leg plates 16 and 18, the motor 44 can be supported by, as necessary, any two or all of the pair of leg plates 16 and 18 and the back plate 14. As a result, a particular improvement in strength for supporting the motor 44 is rendered unnecessary and, as a result thereof, it will be possible to achieve a reduction in weight of the retractor and a reduction in costs.

In the webbing retractor 10 relating to the present embodiment, the gear 76, which serves as the final spur gear of the motor gear section 46, and the worm gear 34 of the clutch gear section 28 are detachably coupled. Therefore, it is possible to detach and replace the motor gear section 46 independently of the clutch gear section 28. Accordingly, it is possible to, for example, easily replace and employ another motor gear section 46, which differs in that tooth counts of the plurality of spur gears, the pinion 72, the gear 74 and the gear 76 or the like, and numbers thereof and the like are altered. Thus, it is possible to easily alter and specify a transmission ratio (reduction ratio) of driving force which is transmitted from the motor 44 to the clutch 26, and it will be possible to easily implement specification and alteration of a speed of rotation transmitted to the clutch 26 when the motor 44 drives, and hence of a speed of rotation of the winding shaft 20 (specification of variations in webbing winding characteristics).

Further, it is possible to detach and replace the motor gear section 46 independently of the clutch gear section 28. Therefore, even in a case of replacing and altering the motor gear section 46 in order to alter the transmission ratio (reduction ratio) as described above or the like, neither of a meshing state of the plurality of spur gears of the motor gear section 46 and a meshing state of the worm gear 34 with the gear wheel 32 of the clutch gear section 28 will be altered (no effect will be applied). Accordingly, there will be no alteration in meshing accuracy of the respective teeth (gears), and there will be no reduction (deterioration) in efficiency of transmission of the driving force.

When this webbing retractor 10 vibrates, torsional force is applied to the above described case 30 and/or the one leg plate 16, to which the same is attached in the joined state, due to heavy components such as the motor 44.

However, the webbing retractor 10 relating to the present embodiment is a structure in which the housing 48, to which the motor 44 is attached, faces in the axial direction of the worm gear 34, and is assembled and fixed to the end face of the case 30 which is orthogonal to the thickness direction of the case 30 (the end face parallel with the back plate 14), and at the side opposite from the back plate 14. Therefore, rigidity in the direction of thickness of the case 30 and a direction intersecting therewith is higher, and it is possible to reliably withstand even torsion forces at the aforementioned times of vibration and the like.

Further, the webbing retractor 10 relating to the present embodiment is a structure in which, of the plurality of spur gears of the motor gear section 46 accommodated in the housing 48, the gear 76 serving as the final spur gear is coupled with the worm gear 34 of the clutch gear section 28. Additionally, the housing 48 is a structure which is assembled and fixed to face in the direction intersecting the direction of thickness of the case 30, that is, the axial direction of the worm gear 34. Moreover, this is a structure in which the positioning bosses 85, which are protrudingly formed at the mounting stays 84 of the housing 48, are fitted into the positioning holes 87, which are formed at the end face of the case 30, thereby positioning and fixing the housing 48 to the case 30. Therefore, dimensional variations in a direction of assembly of this assembly fixing portion of the housing 48 will not affect a pitch (meshing state) of the gear 76, which is coupled with the worm gear 34, with the other gear 74. Accordingly, there is no alteration in meshing accuracy of the respective teeth (gears), and there is no reduction (deterioration) in efficiency of transmission of the driving force.

According to the present invention, a webbing retractor is made more compact, weight balance is good and, moreover, a strengthening of rigidity can be achieved. Thus, it is possible to employ this as a structural member for providing a motor retractor which is reduced in size, of which overall weight balance is good, and which has rigidity capable of withstanding torsion forces caused by vibrations of a motor. 

1. A webbing retractor comprising: a frame formed of a pair of leg plates facing one another and a back plate, the frame being a single body at which the pair of leg plates are continuous with the back plate; a winding shaft which is rotatably supported between the pair of leg plates with an axial direction thereof being along a direction of facing of the pair of leg plates, at which a base end portion of a webbing belt for restraining a vehicle occupant is engaged, and which winds up the webbing belt by rotation in one direction about its axis; a gear housing; a motor attached at the gear housing, which is disposed between the pair of leg plates in a state in which a rotation shaft thereof is orthogonal to the winding shaft; a motor gear section accommodated in the gear housing, which is formed of a plurality of spur gears, axes of which are disposed parallel with the rotation shaft of the motor, and which are coupled with the rotation shaft of the motor; a clutch case attached in a joined state at a side face of any one leg plate of the pair of leg plates; a clutch accommodated in the clutch case, which is mechanically interposed between the motor and the winding shaft, which transmits rotation of the motor to the winding shaft and causes the winding shaft to rotate, and which blocks transmission of rotation which occurs at the winding shaft side and prevents this rotation being transmitted to the motor; and a clutch gear section accommodated in the clutch case, the clutch gear section comprising a worm gear, an axis of which is disposed parallel with the rotation shaft of the motor and which is detachably coupled with a final spur gear of the motor gear section, and a worm wheel, which is disposed coaxially with the winding shaft, meshes with the worm gear and transmits rotation force of the worm gear to the clutch, wherein the gear housing faces in an axial direction of the worm gear, and is assembled and fixed to an end face of the clutch case which is orthogonal to a direction of thickness of the clutch case, at a side which is opposite from the back plate.
 2. The webbing retractor recited in claim 1, wherein a coupling screw is provided at one end of the clutch case side of the winding shaft, and the coupling screw passes through a leg plate at which the clutch case is attached, protrudes into the clutch case, and is connected with the clutch.
 3. The webbing retractor recited in claim 1, wherein the motor is disposed so that a distal end of an output direction of the rotation shaft thereof is oriented toward the gear housing.
 4. The webbing retractor recited in claim 3, wherein the output direction distal end of the rotation shaft of the motor passes through the gear housing and protrudes, and meshes with one of the spur gears of the motor gear section.
 5. The webbing retractor recited in claim 1, wherein a mounting stay is formed at the gear housing, and at least one positioning portion is provided at the mounting stay, a positioning holding portion corresponding to the positioning portion is provided at the clutch case end face at which the gear housing is fixed, and an assembly position of the gear housing is positioned by fixing the gear housing such that the positioning portion of the gear housing and the positioning holding portion of the clutch case end face correspond.
 6. The webbing retractor recited in claim 5, wherein the positioning portion is a boss and the positioning holding portion is a hole. 